(1) Field of the Invention
The present invention relates to peptide analogs of oxyntomodulin (OXM, glucagon-37), which have been modified to be resistant to cleavage and inactivation by dipeptidyl peptidase IV (DPP-IV) and to increase in vivo half-life of the peptide analog while enabling the peptide analog to act as a dual GLP-1/glucagon receptor (GCGR) agonist, and the use of such peptide analogs for treatment of metabolic disorders such as diabetes and obesity.
(2) Description of Related Art
The hormone oxyntomodulin (OXM, glucagon-37) is a posttranslational product of preproglucagon processing in the intestine and central nervous system (CNS) and is secreted from L-cells in the gut in response to food intake. Discovered in 1983, OXM has been implicated in the regulation of food intake and energy expenditure (Jarrouse et al., Endocrinol. 115: 102-105 (1984); Schjoldager et al., Eur. J. Clin. Invest., 18: 499-503 (1988)). Central or peripheral administration of OXM in rats causes a decrease in short term food intake with minimal effects on gastric emptying (Dakin et al. Endocrinology, 142: 4244-4250 (2001), Dakin et al. Endocrinology, 145: 2687-2695 (2004)). Repeated intracerebroventricular administration of OXM in rats results in elevated core temperatures and reduced weight gain compared to pair-fed animals, suggesting effects on both caloric intake and energy expenditure (Dakin et al. Am. J. Physiol. Endocrinol. Metab., 283: E1173-E1177 (2002)).
In related studies, peripheral administration of OXM dose-dependently inhibited both fast-induced and dark phase food intake, but unlike GLP-1, had no effect on gastric emptying. OXM also reduced levels of fasting ghrelin and increased c-fos immunoreactivity, in the arcuate nucleus (ARC). Repeated seven-day IP administration of OXM caused a reduction in the rate of body weight gain and adiposity in rats (See Dakin et al. Endocrinology, 145: 2687-2695 (2004)).
Studies of OXM action in mice have demonstrated that although OXM can activate both the glucagon and GLP-1 receptors, the anorectic actions of OXM require only the GLP-1 receptor, as icy OXM inhibits food intake in glucagon receptor knockout mice. However, the anorectic effects of OXM are completely absent in GLP-1 receptor knockout mice. Furthermore, exendin-4, but not OXM, regulates energy expenditure in mice. Hence, OXM appears to be a weak agonist at the GLP-1 receptor, when used in pharmacological concentrations (See Baggio et al., Gastroenterol. 127: 546-58 (2004)). OXM was also found to ameliorate glucose intolerance in mice fed a high fat diet (Dakin et al., Am. J. Physiol. Endocrinol. Metab. 294: E142-E147 (2008) and increase the intrinsic heart rate in mice independent of the GLP-1 receptor (Sowden et al., Am. J. Physiol. Regul. Integr. Comp. Physiol. 292: R962-R970 (2007). OXM has also been shown to differentially affect GLP-1 receptor beta-arrestin recruitment and signaling through Galpha (Jorgensen et al., J. Pharma. Exp. Therapeut. 322: 148-154 (2007)) and to differentially affect hypothalamic neuronal activation following peripheral injection of OXM (Choudhri et al., Biochem. Biophys. Res. Commun. 350: 298-306 (2006)).
In humans, a single 90 minute intravenous infusion of OXM in normal weight healthy subjects reduced hunger scores and food intake at a buffet meal by about 19%. Cumulative twelve-hour caloric intake was reduced by about 11% with no reports of nausea or changes in food palatability (Cohen et al., J. Clin. Endocrinol. Metab., 88: 4696-4701 (2003); Lykkegaard et al., ADA Scientific Sessions, Abstract #1506-P (2003)). More recently, pre-prandial injections of OXM over a four-week period in obese healthy volunteers (BMI about 33) led to a significant reduction of caloric intake on the first day of treatment (about 25%) that was maintained over the course of the study (35% reduction after four weeks) (Wynne et al., Diabetes 54: 2390-2395 (2005)). Robust weight loss was observed at the end of the study in treated subjects (1.9%, placebo-corrected). Plasma levels of OXM were similar to that observed in the infusion study (peak concentration about 950 pM). The absence of any tachyphylaxis and a low incidence of mild and transient nausea (about 3%) despite the relatively high doses necessitated by the poor in vivo stability of OXM (plasma t1/2<12 minutes) renders this hormone one of the few obesity targets with both human validation and an attractive tolerability profile.
OXM has a very short half-life and is rapidly inactivated by the cell surface dipeptidyl peptidase IV (DPP-IV) (Zhu et al., J. Biol. Chem. 278: 22418-22423 (2002). However, DPP-IV inhibitors are weight-neutral in the clinic, suggesting that supraphysiological levels of OXM (900-1000 pM) may be required to achieve weight loss in humans. OXM peptide analogs for inducing weight loss in humans has been the object of Published International Application Nos. WO03/022304, WO2004/062685, and WO2006/134340.
OXM therefore shows potential as a treatment for metabolic disorders such as diabetes and obesity. However, because of the poor in vivo stability of OXM, there exists a need to develop OXM analogs that can be safely and efficaciously administered for the treatment of metabolic diseases, such as diabetes and obesity. It would be further desirable if analogs or derivatives were developed that were modified by conjugation to moieties that would improve stability and pharmacokinetics, more particularly modifications that confer resistance to DPP-IV cleavage. It would further be desirable to provide OXM analogs that are capable of acting as dual GLP-1 receptor/glucagon receptor agonists.